1. Field of the Invention
The present invention relates generally to a system and method for operating a motor vehicle. More particularly, the invention relates to a method for preventing a reverse run condition of an internal combustion engine.
2. Background Art
When starting conventional motor vehicle having an internal combustion engine, if the ignition key is released from the starter position before the engine has begun to run, the engine may stop forward rotation near the top of a compression stroke and rock backwards. The stopping position is generally at or near the position at which spark is requested. If a spark is fired before top dead center (TDC) on a cylinder which is no longer moving forward, the engine is powered backward. Given the proper combination of conditions, successive sparking may occur thus resulting in a xe2x80x9creverse runningxe2x80x9d condition of the engine. Under this condition, an induction xe2x80x9cbackfirexe2x80x9d condition may occur resulting in relatively high pressures being generated in the intake manifold and surrounding engine components.
Thus, in order to prevent reverse running of the engine and other conditions that may result in inappropriate ignition of an air/fuel mixture, it is desirable when starting the vehicle to know whether the starter motor is engaged or disengaged. By knowing whether the starter is disengaged, for example, a vehicle""s control system can be operated to cease fuel supply and/or deactivate spark control so as to avoid a reverse run condition and corresponding backfire potential of the engine.
Although conventional control systems are provided with specialized crankshaft position sensors that are able to distinguish between forward and backward rotation of the crankshaft, such sensors are costly and generate signal content that add undesirable computational complexity at higher engine speeds.
Accordingly, the inventors herein have recognized a need for determining whether a reverse run condition exists or is likely to occur without using complicated sensors and computational techniques.
The aforedescribed limitations of conventional electronic ignition automobile starting methods are substantially overcome by the present invention, in which a method is provided for preventing reverse running of an internal combustion engine. The preferred method of the present invention includes the steps of determining the operational state of the vehicle starter motor, determining whether a stall or imminent stall condition exists, and suspending operation of the engine based on the stall or imminent stall condition. Preferably, the step of determining the operational state of the vehicle starter motor includes the step of inferring whether the starter motor is engaged or disengaged.
Advantageously, by combining engine starter status information and calibrated engine speed thresholds to determine whether stall or imminent stall conditions exist, undesirable reverse running of an internal combustion engine is avoided while eliminating complicated processing of sensor signals. In accordance with a preferred method, the engine starter status is inferred. The disclosed method and corresponding system can therefore be used advantageously to cut-off spark control and fuel supply before an undesired xe2x80x9cbackfirexe2x80x9d ignition of the air/fuel mixture occurs.